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OpenAI · Frontier

GPT 5.3 Codex

Added Feb 24, 2026

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Use in the app

Coding-focused GPT-5.3 variant with optimized routing.

  • Reasoning
  • Tools
  • Vision
  • Structured output
  • PDF input
Input
Text, Images
Output
Text
Reasoning effort
low · medium · high · xhigh
Discovery tier
Frontier

Pricing

USD per 1M tokens
Input
$1.75
Output
$14.00
Cache read
$0.18

Reference prices as published by the model provider. API example

Specifications

Context window
400K
Max output
128K
Average output (7 days)
281 tokens
Longer than 29% of 465 models

Side by side

GPT 5.3 Codex compared

Specifications, prices, speed and benchmark scores next to each other. Benchmarks below show every compared model too.

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GPT 5.3 CodexOpenAIThis modelGemini 3.5 FlashGoogleRemove
ProviderOpenAIGoogle
Discovery tierFrontierEfficient
AddedFeb 24, 2026May 19, 2026
Limits
Context window400K1.05MBest
Max output128KBest65.54K
Average output281 tokens322 tokens
Pricing, USD per 1M tokens
Input$1.75$1.50Best
Output$14.00$9.00Best
Cache read$0.18$0.15Best
Cache write—$0.0833
Performance
Throughput—264.0 tok/s
Time to first token—4.8 s
Request success (24h)98.5%Best98.0%
Benchmark indexes
Intelligence Index32.532.6Best
Coding Index—70.1
Capabilities
ReasoningYesYes
ToolsYesYes
VisionYesYes
Structured outputYesYes
PDF inputYesNo
Audio inputNoYes
Video inputNoYes
Reasoning effortlow, medium, high, xhighminimal, low, medium, high

Public evaluations

Benchmarks

Independent evaluation results, with how each score ranks among the models in the Noumen catalog.

  • GPT 5.3 Codex
  • Gemini 3.5 Flash

Intelligence Index

  • GPT 5.3 Codex32.5
  • Gemini 3.5 Flash32.6

GPT 5.3 Codex tested at xhigh reasoning effort

GPT 5.3 Codex: Better than 76% of 326 scored models

3.8Catalog models by score55.1

Indexes

  • Coding Index

    Composite of the coding evaluations

    • GPT 5.3 Codex: —
    • Gemini 3.5 Flash: 70.1

Agentic work

  • AutomationBench-AA

    Workflow automation, penalized for guardrail violations

    • GPT 5.3 Codex: —
    • Gemini 3.5 Flash: 42.1%

  • AutomationBench-AA tasks completed

    Workflows finished end to end without a guardrail violation

    • GPT 5.3 Codex: —
    • Gemini 3.5 Flash: 13.5%

  • AA-Briefcasev1.1

    Agentic knowledge work, rated head to head

    • GPT 5.3 Codex: 868 Elo
    • Gemini 3.5 Flash: 874 EloTop

  • GDPval-AAv2.1

    Economically valuable occupational tasks, rated head to head

    • GPT 5.3 Codex: —
    • Gemini 3.5 Flash: 1,202 Elo

Document reasoning

  • GDP.pdf

    Professional reasoning over PDF documents, all-pass rate

    • GPT 5.3 Codex: —
    • Gemini 3.5 Flash: 19.8%

  • AA-LCRv1.1

    Reasoning across long documents

    • GPT 5.3 Codex: 83.3%Top
    • Gemini 3.5 Flash: 73.3%

  • MLCR-AA

    Long-context reasoning over medical records

    • GPT 5.3 Codex: —
    • Gemini 3.5 Flash: 10.0%

Reasoning and knowledge

  • Humanity’s Last Exam

    Expert-level questions across academic fields

    • GPT 5.3 Codex: 42.5%
    • Gemini 3.5 Flash: 42.7%Top

  • GPQA Diamond

    Graduate-level science questions

    • GPT 5.3 Codex: 91.5%
    • Gemini 3.5 Flash: 92.2%Top

  • IFBench

    Following precise output instructions

    • GPT 5.3 Codex: 75.4%
    • Gemini 3.5 Flash: 76.3%Top

Coding

  • Terminal-Benchv4.0

    Practical software engineering in a terminal

    • GPT 5.3 Codex: —
    • Gemini 3.5 Flash: 6.6%

  • SciCode

    Scientific computing in Python

    • GPT 5.3 Codex: —
    • Gemini 3.5 Flash: 53.9%

Legacy evaluations

  • Terminal-Bench Hard

    Earlier terminal task suite

    • GPT 5.3 Codex: 53.0%Top
    • Gemini 3.5 Flash: 40.9%

  • τ²-Bench Telecom

    Tool use in a customer-support simulation

    • GPT 5.3 Codex: 86.0%
    • Gemini 3.5 Flash: 95.3%Top

  • AA-LCR (unversioned)

    Long-context reasoning, earlier grading

    • GPT 5.3 Codex: 83.3%Top
    • Gemini 3.5 Flash: 73.3%

Scores from Artificial Analysis, updated Oct 26, 2026. GPT 5.3 Codex was tested at xhigh reasoning effort; compare scores measured at the same effort.Artificial Analysis

Live routing data

Performance and reliability

Recent averages across requests routed for this model. Your own speed depends on prompt length, reasoning effort and load.

Prompt cache hits
7.7%
About $1.63 per 1M input tokens with caching
Request success (24h)
98.5%
Reliable

Cache hits are the share of input tokens recently served from a prompt cache across all requests. They are not a forecast of your own hit rate.

Hourly request success · last 72 hoursLowest hour 97.4%
  • Healthy (98% or more)
  • Degraded (90–98%)
  • Down (under 90%)
  • No requests

Developers

Use it through the API

Noumen’s API is OpenAI-compatible: any Chat Completions client works with a base URL and a key.

Read the quickstart
curl https://www.noumen.xyz/api/v1/chat/completions \
  -H "Authorization: Bearer $NOUMEN_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "model": "openai/gpt-5.3-codex",
    "reasoning_effort": "medium",
    "messages": [{ "role": "user", "content": "Explain this stack trace." }]
  }'
import os
from openai import OpenAI

client = OpenAI(base_url="https://www.noumen.xyz/api/v1", api_key=os.environ["NOUMEN_API_KEY"])
reply = client.chat.completions.create(
    model="openai/gpt-5.3-codex",
    messages=[{"role": "user", "content": "Explain this stack trace."}],
)
print(reply.choices[0].message.content)

OpenAI

Other OpenAI models, starting with the same family.